The invention discloses a servo motor power line wiring phase sequence error detection method, which is characterized by determining maximum output torque Tmax of a servo motor; obtaining a torque observed value TL through a disturbance observer; judging whether the torque observed value TL surpasses detection threshold M; and if the amplitude of the load torque TL exceeds the maximum output torque Tmax of the servo system, determining that the motor power line phase sequence is wrong. The method realizes on-line detection of the servo motor power line phase sequence error; the detection process is automatically completed by a servo driver without additional operation of operators; and when an error is found, an alarm is given and a motor is enabled to stop operating, thereby preventing high-speed uncontrolled operation of the motor. The torque observed value of the load is obtained through the disturbance observer, thereby improving detection reliability and real-time performance; andno extra hardware cost is needed, and only a detection algorithm is added to motor controllers, such as the servo driver and a frequency converter, so that the method is easy to realize engineering realization.